1. Field of the Invention
The present invention relates generally to a method for controlling a wireless power transmitter and a wireless power receiver, and more particularly, to a method for controlling a wireless power transmitter and a wireless power receiver which communicate with each other in a predetermined communication scheme.
2. Description of the Related Art
In view of their nature, mobile terminals such as portable phones and Personal Digital Assistants (PDAs) are powered by rechargeable batteries. To charge the batteries, the mobile terminals apply electrical energy to the batteries via chargers. Typically, the charger and the battery each have an exterior contact terminal and thus are electrically connected to each other via their contact terminals.
This contact-based charging scheme faces the problem of vulnerability of contact terminals to contamination of foreign materials and the resulting unreliable battery charging because the contact terminals protrude outward. Moreover, if the contact terminals are exposed to moisture, the batteries may not charge properly.
To address the above problem, wireless charging or contactless charging technologies have recently been developed and applied to many electronic devices.
Such a wireless charging technology is based on wireless power transmission and reception. For example, once a portable phone is placed on a charging pad without being connected to an additional charging connector, its battery is automatically charged. Among wirelessly charged products, wireless electric toothbrushes and wireless electric shavers are well known. The wireless charging technology offers the benefits of increased waterproofness due to wireless charging of electronic products and enhanced portability due to no need for a wired charger for electronic devices. Further, it is expected that various relevant wireless charging technologies will be further developed in the upcoming era of electric vehicles.
There are mainly three wireless charging schemes: electromagnetic induction using coils, resonance-based charging, and Radio Frequency (RF)/microwave radiation based conversion of electrical energy to microwaves.
To date, the electromagnetic induction-based wireless charging scheme has been most popular. However, considering recent successful experiments in wireless power transmission over microwaves at a distance of tens of meters in Korea and other countries, it is foreseeable that every electronic product will be charged wirelessly at any time in any place in the near future.
Electromagnetic induction-based power transmission refers to power transfer between primary and secondary coils. When a magnet moves through a coil, current is induced in the coil. Based on this principle, a transmitter creates a magnetic field and a receiver produces energy by current induced by a change in the magnetic field. This phenomenon is called magnetic induction and power transmission based on magnetic induction is highly efficient for energy transfer.
In 2005, regarding resonance-based wireless charging, a system that makes wireless energy transfer from a charger at a distance of a few meters based on the resonance-based power transmission principle by the Coupled Mode Theory was developed. This wireless charging system is based on a physics concept that an oscillating tuning fork placed next to a wine glass will cause the wine glass to oscillate at the same frequency of the tuning fork. The team resonated electromagnetic waves carrying electric energy, instead of sound. The resonant electrical energy is directly transferred only in the presence of a device having the same resonant frequency, while the unused electric energy is reabsorbed into the electromagnetic field rather than being transmitted. Thus the resonant electrical energy does not affect nearby machines or human bodies, as compared to other electrical waves.
Wireless charging is a recent area of active research. However, there are no specified standards of wireless charging priority, detection of a wireless power transmitter/receiver, communication frequency selection between a wireless power transmitter and a wireless power receiver, wireless power control, selection of a matching circuit, and allocation of a communication time to each wireless power receiver in a single charging cycle. Particularly, there exists a need for developing standards for a configuration and procedures that allow a wireless power receiver to select a wireless power transmitter from which to receive wireless power.
A wireless power transmitter and a wireless power receiver may communicate with each other in a predetermined communication scheme, for example, by ZigBee or Bluetooth Low Energy (BLE). Such an out-of-band scheme such as ZigBee or BLE increases an available communication distance. Accordingly, even if a wireless power transmitter and a wireless power receiver are relatively far from each other, they may communicate. In other words, even if the wireless power transmitter is too far to transmit power wirelessly, the wireless power transmitter may communicate with the wireless power receiver.
Referring to FIG. 1, a first wireless power transmitter TX1 and a second wireless power transmitter TX2 are deployed. A first wireless power receiver RX1 is placed on the first wireless power transmitter TX1 and a second wireless power receiver RX2 is placed on the second wireless power transmitter TX2. The first wireless power transmitter TX1 should transmit power to the nearby first wireless power receiver RX1 and the second wireless power transmitter TX2 should transmit power to the nearby second wireless power receiver RX2. Accordingly, the first wireless power transmitter TX1 preferably communicates with the first wireless power receiver RX1 and the second wireless power transmitter TX2 preferably communicates with the second wireless power receiver RX2.
According to an increase in communication distance, the first wireless power receiver RX1 may join a wireless power network managed by the second wireless power transmitter TX2, while the second wireless power receiver RX2 may join a wireless power network managed by the first wireless power transmitter TX1. This is called cross-connection. As a result, the first wireless power transmitter TX1 may transmit power requested by the second wireless power receiver RX2 instead of the first wireless power receiver RX1. If the capacity of the second wireless power receiver RX2 is greater than the capacity of the first wireless power receiver RX1, the first wireless power receiver RX1 may experience overcharging. On the other hand, if the capacity of the second wireless power receiver RX2 is less than the capacity of the first wireless power receiver RX1, the first wireless power receiver RX1 receives power below its charging capacity (e.g. undercharging).